The field of the disclosure relates generally to radiofrequency identification (RFID) systems. More particularly, the present disclosure relates to passive RFID assisted active RFID tags and methods therefor.
RFID is a technology that allows a wide range of objects to be identified, tracked and managed. RFID technology is based on the use of small radio tags or transponders and readers/encoders for connection to an information system. These RFID tags, which contain a unique code together with other additional information, can be read by the reader/encoder from a distance without contact or line-of-sight. Typical RFID are categorized as either active or passive.
Active RFID tags are typically powered by an internal battery and may include read/write functionality (i.e., tag data can be rewritten and/or modified). An active RFID tag's memory size may vary according to application requirements. In a typical active RFID system, the RFID tag might periodically transmit its data, including a part number and location to a central tracking database. The battery-supplied power of an active tag generally gives it a longer read range than a passive RFID tag. However, active RFID tags result in greater size, greater cost, and an operational life limited to about 10 years depending on operating temperatures and battery type, as compared to passive RFID tags. Additionally, active RFID tags are typically not suitable for indoor use, due to limitations and inherent unreliability of using traditional received signal strength indicators (RSSI) and time distance of arrival (TDOA) calculations.
Passive RFID tags operate without an internal power source. The passive RFID tags obtain operating power from the electromagnetic transmissions generated by the reader. Consequently, passive tags may be much lighter than active tags, less expensive, and offer a virtually unlimited operational lifetime. Passive tags are typically read-only and are programmed with a unique set of data that cannot be modified. However, passive tags may also be read/write tags that are initially programmed with a unique set of data and such data may be modified and updated at desired intervals. In order to operate, the passive tag reader must initiate the communication to the tag, and the tag then responds with its identifier. Typically, to obtain the location of the passive tag, the reader may use a combination of previous known location of the tag, RSSI and TDOA between the tag and reader, triangulation antenna gain measurement. Thus, passive RFID tags generally result in more accurate location of the tags as compared to active tags. Although cheaper and smaller than active tags, passive tags have shorter read ranges than active tags and require a higher-powered reader.
The advantage of RFID systems is the non-contact, non-line-of-sight nature of the technology. Tags can be read through a variety of substances, including metal, where barcodes or other, traditional optically read technologies would be impractical.